Present inventories of solid rocket motor (SRM) propellant slated for disposal are over 164 million pounds and increasing due to the imminent disposal requirements of the Strategic Arms Reduction Treaty. Additionally, almost 7 million pounds of waste propellant are generated annually in the U.S. as a by-product of manufacturing. Over 500,000 tons of ordnance items are stockpiled and awaiting disposal. These propellants and explosives are hazardous waste due to their inherent reactive and toxic natures.
Because these materials are complex cross-linked composites, with components that are partially or completely soluble in water, they are difficult to reclaim and reuse. Historically, open burning (OB) and open detonation (OD) have been used to dispose of these materials. However, under Resource Conservation and Recovery Act (RCRA), OB/OD has been severely limited and, in some cases, totally prohibited.
Ammonium perchlorate is the primary ingredient in most rocket propellants and is also present in lesser quantities in many ordnance items. The U.S. Environmental Protection Act (EPA) recently established a provisional reference dose for perchlorate of 32 parts-per-billion (ppb). This has caused the California Department of Health Services to close 23 drinking water wells in southern and northern California.
Separation or concentration of perchlorate in drinking water and disposal by biodegradation is one possible solution to the problem. Safe ways of containing and destroying energetic materials and wastewater generated from disposal and production activities is critically important to continued use of these materials in our nation's weapon systems.
In addition to treating perchlorate in the presence of salts and other energetic materials, other energetics themselves (nitramines, nitroglycerin, nitrates, nitroaromatics, etc.) must be destroyed. Processes to treat energetic materials must be robust, predictable, and cost-effective.
A method for treatment of such contaminated wastewater is disclosed in U.S. Pat. No. 5,302,285. The method involves reduction of perchlorate to chloride in a first stage anaerobic reactor, using a specific microorganism in mixed culture, followed by treatment of the organics produced in the first reactor in a second stage aerobic reactor. The specific microorganism is designated as HAP1 and was classified as being strictly anaerobic.
It was recently discovered that the bacterium Wolinella succinogenes can effectively reduce perchlorate (Wallace, W., Ward, T., Breen, A., Attaway, H. 1996 "Identification of an Anaerobic Bacterium Which Reduces Perchlorate and Chlorate as Wolinella succinogenes". Journal of Industrial Microbiology, 16:pp. 68-72). Although originally categorized as being an anaerobe in Bergey's Manual of Systematic Bacteriology, Vol. 1, Wolinella sp. is in fact capable of respiring with oxygen. It has also been subsequently recognized as a H.sub.2 and formate requiring microaerophile (Bergey's Manual of Determinative Bacteriology, Ninth Edition, 1994).
Prior to the present invention the use of such a microorganism in the treatment of perchlorate contaminated wastewater had only been carried out in a two stage anaerobic-aerobic process. Such a process was capable of reducing perchlorate wastewater concentrations of 7750 mg per liter.
It has been surprisingly found, however, that wastewater contaminated with perchlorate, and other energetic materials, including hydrolysate products of energetic compounds, can be more effectively treated using a controlled microaerobic environment.
By the use of the present invention and the use of a controlled microaerobic environment as opposed to a strictly anaerobic, aerobic or anoxic environment, certain advantages over the prior art are realized. In particular, the invention is (1) capable of reducing higher perchlorate concentrations, greater than 9000 mg/l in a single stage reactor system and greater than 15,000 mg/l in a multi-stage system; (2) capable of higher reduction rates than previously reported, greater than 0.7 g/l per hour; (3) capable of reducing anions (ClO.sub.4.sup.-, ClO.sub.3.sup.-, NO.sub.3.sup.-, NO.sub.2.sup.-) in the presence of high salt concentrations (&gt;3.4% total dissolved solids); (4) capable of reducing perchlorate and alkaline hydrolyzed energetics simultaneously; (5) capable of reducing greater than 18,000mg/l of nitrate (NO.sub.3.sup.-) in a single stage system; (6) capable of maintaining anion (ClO.sub.4.sup.-, ClO.sub.3.sup.-, NO.sub.3.sup.-, NO.sub.2.sup.-) reducing capability over extended periods (&gt;2 weeks), without anions present; (6) capable of maintaining ClO.sub.4.sup.- reduction capability at ClO.sub.4.sup.- concentrations of &lt;1.5 ppm; (7) capable of effectively using low-cost nutrients (e.g., cheese whey, whole yeast, milk and brewery waste and sugar/starch-based carbohydrate wastes, etc.,) and combinations of low-cost nutrients; (8) capable of effectively treating contaminated ground water with or without a preliminary concentration step; (9) capable of reducing anions (ClO.sub.4.sup.-, ClO.sub.3.sup.-, NO.sub.3.sup.-, NO.sub.2.sup.-)in NaCl brine from ion exchange concentration processes; and (10) capable of effectively reducing chromium VI to relatively insoluble chromium III compounds.
It is therefore an object of the present invention to provide a method for effectively treating wastewaters contaminated with perchlorate, nitrate, hydrolysates and other energetic materials.
It is another object of the present invention to provide a method for reducing perchlorate, nitrate, hydrolysates and other energetic materials present in wastewaters using a specific bacterium, Wolinella succinogenes, in a mixed culture and in a controlled microaerobic environment.
It is a further object of the present invention to provide a method for effectively and easily maintaining a microaerobic environment.
It is also an object of the present invention to treat wastewaters with high concentrations of perchlorate, nitrate, hydrolysates and other energetic materials and at high perchlorate reduction rates, in a simple and cost effective manner.
These and other objects of the present invention will become apparent from the detailed description and examples which follow.